In certain types of circuit applications it has become commonplace to provide for circuit redundancy. Typical of such applications are those where the national defense depends on the reliability of the circuit and those where human lives are dependent on proper circuit performance. For instance, many defense EW and ESM systems are designed to provide circuit redundancy. Additionally, such systems require the use of inherently reliable technologies, such as integrated circuitry rather than discrete components, to the maximum extent feasible. In airborne, spaceborne or remotely placed systems, an effective approach for circuit functions is required that provide the desired reliable performance with graceful degradation, in case of device failure, with cost as a major consideration. Monolithic technology provides inherent reliability relative to discrete components, is generally lower in cost due to the reduction in wire bonding and part count and also provides enhanced reproducibility since there are fewer opportunities to introduce variations into the end product.
Circuit applications requiring switching where redundancy is desired have not been satisfactorily implemented in GaAs technologies due to the absence of a feasible manner of implementing such circuits in GaAs integrated circuits. In the past, fast electronic switches using pin diodes have been designed and have been made redundant by using parallel or series diode pairs to replace single diodes. However, these switches require many discrete components, have high assembly costs, require exotic drivers, consume significant dc power, and allow the switching waveform to couple onto the rf signal path.
According to the present invention, redundancy is provided in a GaAs-based switch which is not dependent on the provision of pin diodes. N-way redundancy can be provided by employing GaAs MESFETs in a novel circuit design approach which is compatible with GaAs integrated circuit manufacturing technology. According to the novel design approach, GaAs MESFETs are arranged in series and shunt configurations in each series and shunt arm such that, if some of the MESFETs fail, the circuit still performs its intended function with very little degradation in the signal quality. A single pole single throw switch is shown in FIG. 2 which includes series connected MESFET shunt switching elements 121, 131 and series connected MESFET switching elements 111 to implement the redundancy feature. FIGS. 3 and 4 respectively illustrate single pole double throw and single pole triple throw switches including both series and shunt connected MESFETs. FIG. 5 illustrates the physical layout of the single pole double throw switch illustrated in FIG. 3.